Although traumatic cerebral vascular injury has been recognized and studied for decades, the contributing mechanisms remain uncertain. Evidence that inhibitors of gap junctions (GJ) attenuate myogenic tone and acetylcholine-mediated vasodilation in cerebral arteries suggests that GJ communication between vascular endothelial and smooth muscle cells plays an important role in cerebral arterial tone and vasodilation. The central hypothesis of this application is that TBI induces traumatic cerebral vascular dysfunction, in part, by generating reactive oxygen species (ROS) that impair GJ communication between endothelial cells and between smooth muscle cells in the cerebral vasculature. Specific Aim I is to determine the effects of TBI on cerebral vascular GJ communications by measuring the rate of fluorescence recovery after photo bleaching (FRAP) and quantifying connexin (Cx) 37,40, 43 and 45 mRNA expression in cerebral arteries harvested from rats subjected to fluid percussion traumatic brain injury. Specific Aim II is to measure, in cultured vascular endothelial and smooth muscle cells, the effects of rapid stretch injury on GJ communication, cell viability and the production of ROS (nitric oxide, NO;peroxynitrite, ONOO-;superoxide anion radical, .O2-). To further test the hypothesis that ROS contribute to trauma-induced GJ impairment, FRAP will be measured in endothelial and smooth muscle cells subjected to rapid stretch injury followed by treatment with scavengers of ONOO- (FeTPPS, penicillamine) or .O2- (superoxide dismutase, SOD) or the inhibitor of NO synthesis (L-nitroarginine methyl ester, L-NAME). Specific Aim III is to measure vasodilator responses to reduced intravascular pressure, calcitonin gene-related peptide, or acetylcholine and vasoconstrictor responses to increased intravascular pressure, serotonin and thromboxane in isolated middle cerebral arteries treated with GJ inhibitors. Specific Aim IV is to measure GJ communication (using FRAP) and Cx mRNA expression in cerebral arteries harvested from rats subjected to traumatic brain injury and treated with SOD, L-NAME, FeTPPS or penicillamine.